The present invention relates in general to insulated enclosures and more particularly to radio frequency shielded and acoustically insulated enclosures.
The power of magnetic resonance imaging (“MRI”) equipment is continually increasing to meet the demand in the medical community for better and faster developing images. However, as the power of MRI equipment increases, an increased amount of noise is generated due, in part, to the coil assembly of the MRI equipment. MRI acoustic noise is mainly caused by Lorentz forces acting on the gradient coils of the MRI equipment. As the gradient current switches direction, the gradient windings vibrate in their mountings, leading to the emission of sound waves. The frequency range for such sound waves for certain MRI equipment may be 10 Hz-20 kHz. MRI equipment therefore generates substantial noise, possibly at different frequencies, which travels from the MRI equipment toward the walls, floor and ceiling of the enclosure in which the MRI equipment resides. The MRI equipment transmits noise: (i) through the air to the walls, ceiling and floor of
As a result, the level of noise may at times exceed health and safety regulatory and industry standards, which seek to protect the operator of the MRI equipment (and others in the surrounding areas adjacent to such rooms or enclosures) from potentially dangerous noise levels. Such MRI equipment must therefore be properly contained within a radio frequency (“RF”) shielded and sufficiently acoustically insulated room to protect the MRI equipment from stray electromagnetic radiation and to protect the operators (and others) from continuous, excessive and undesired noise levels.
To absorb the airborne noises in an RF room or enclosure, manufacturers have employed multiple layers of an insulating material in the walls, ceiling and floor of the enclosure to absorb noise up to a particular decibel level. Generally, adding additional layers or thickening existing layers of the insulating material in the enclosure increases the noise absorption characteristics of the enclosure. Although the addition of the extra layers or extra thickness of the insulating materials increases noise absorption of the enclosure, this method of increasing noise attenuation eventually diminishes in efficiency. That is, as additional layers of the insulation are added, the level of noise absorption reaches a plateau, whereby adding additional layers of the insulating material to the enclosure will not overcome the plateau.
For example, a known type of sound insulation is chipboard or particleboard core sheet. It is also known that 50 mm of a certain type of particleboard provides 28 decibels (dB's) of attenuation. 60 mm of the same type of particleboard provides 29 decibels (dB's) of attenuation. 80 mm of the same type of particleboard provides 32 decibels (dB's) of attenuation, etc. As illustrated, the change in attenuation lessens as the particleboard thickens.
Adding layers of insulation or thickening layers begins to take up substantial space and adds to the cost and weight of the enclosure. Therefore, simply adding extra layers of the insulating material or thickening the existing layers increases the cost of the enclosure without maximizing the noise absorption capability of the enclosure.
To better absorb airborne noises from MRI equipment, there is a need for an RF shielded and acoustically insulated enclosure which attenuates RF fields and absorbs increased levels of noise in an efficient, cost effective and spatially acceptable manner.
Additionally, the MRI equipment presents a related noise and vibration problem because the MRI equipment transmits vibration and noise through the supporting floor. The floor below the MRI equipment must therefore support the weight of the magnet present in the MRI equipment and the vibration generated by the MRI equipment. Simply providing layers of sound insulation does not effectively prevent the vibration and related noise from traveling from the equipment through such supports, to the I-beams and other support structures that separate one room from another and one floor from another in the building which houses the RF enclosure. Accordingly, there is a need for an RF shielded and acoustically insulated enclosure that absorbs the vibration and related noise generated by the MRI equipment.